A priming chamber consists of a receptacle designed to accommodate the priming capsule and it is housed in the base of a cartridge case. One type of priming chamber currently used comprises two elements: a cylindrical envelope and an anvil designed to resist the force exerted by the impact element of a firearm.
In a known implementation (see, for example U.S. Pat. No. 4,029,015), the anvil forms an integral part of the cylindrical envelope and the priming chamber comprises a single element. In this embodiment, the anvil has a tapered body, for example conical or pyramidal in shape with a flat end. The lower part of the anvil body, which is connected to the cylindrical envelope, is pierced with a plurality of flash-holes a vent holes disposed around the circumference of the anvil and separated from one another with a predetermined angular spacing. These flash-holes permit the passage of the heat generated by the explosion of the primer resulting from the impact, in order to transfer it to the powder held in the cartridge case so as to effect the propulsion of the projectile.
With this type of priming chamber, it is frequently observed that the powder has difficulty in igniting and the projectile has a relatively low velocity. These flaws are attributed to the arrangement of the flash-holes, which, being disposed along the cylindrical envelope, transfer heat in the direction of the powder in the form of narrow waves of heat which are clearly separated from one another around the circumference of the priming chamber.